Hydraulic lash adjuster



Nov. 12, 1957 K. w. LEsHl-:R 2,812,750

HYDRAULIC LASH ADJUSTER Filed 0G13. l, 1956 z Z0 i W UMIL! i IN V ENTOR;

BY M v L United States Patent O f' HYDRAULIC LASH ADJUSTER Kenneth W.Lesher, Grand Rapids, Mich., assigner zo General Motors Corporation,Detroit, Mich., a corporation of Delaware Application October` 1, 1956,`Serial No. 613,132

` s Claims. (C1. 12s-.99)

This invention relates `to hydraulic lash adjusters as, for example,those used in the valve operating linkages of in'- ternal combustionengines to transmit the valve opening movement without lash (lostmotion) between the valve and the cam or other valve operating member.

in conventional hydraulic lash adjusters of .this general type themotion of the cam is transmitted to the engine valve through a cylinderand Slidably inter-tted plunger resting on a body of hydraulic fluidcontained in the cylinder. The fluid used may be the engine lubricatingoil, supplied to thelash adjuster by the engine oil pump. The amount offluid introduced `into the lash adjuster below the plunger isautomatically controlled by suitable valving within the adjuster inaccordance with thermal expansion and wear occurrin-g in the variousparts of the valve linkage to maintain a zero lash in the system.Difficulty is encountered, however, at high engine operating speeds inpreventing a condition called pump-up which occurs when too much oilgets below the plunger and results in extending the operating length ofthe lash adjuster sui ciently to prevent normal closing of the enginevalve. The undesirable effects of this are usually oversheating of thevalve, loss of engine power, etc. I have found this difficulty can beeliminated by a unique arrangement of valving the admission and escapeof oil from a cylinder chamber below the plunger, whereby excessivefluid pressures which might otherwise occur in this chamber incident topump-up are prevented. As a result, the lash adjuster in accordance withmy invention enables obtaining satisfactory engine operation at speedsconsiderably above those possible heretofore.

it is therefore the principal object of my invention to provide ahydraulic lash adjuster having improved operating characteristics,particularly in respect to increasing the operating speeds thereofwithout incurring pump-up.

It is a further object to effect this improvement in a manner which issimple and does not increase the cost of the lash adjuster beyond whatis commercially acceptable.

The means by which these and other objects of my invention areaccomplished will be readily apparent from the following description ofa preferred embodiment thereof selected for purposes of illustration,wherein:

Figure l is a sectional View of a portion of an internal combustionengine having a valve operating linkage including my improved hydrauliclash adjuster.

Figure 2 is an enlarged view similar to Figure l showing details of alash adjuster with parts broken away and in section.

Referring now in detail to the drawing, the numeral 1 designates aconventional cylinder block and cran-kcase of an internal combustionengine having one or more cylinders 2, in each of which is fitted areciprocating piston 3. Shown reciprocally mounted in the cylinder head4 above the piston is a poppet valve 5 which controls the inlet (orexhaust) for the cylinder 2. The valve 5 is normally held in closedposition, as shown, by the valve spring 6, and during engine operationit is intermittently 2,812,750 Patented Nov. 12, 1957 rice moveddownwardly to its open position against the valve spring by the valveoperating cam 7, whose motion is transmitted to the upper end 8 of thevalve through my hydraulic lash adjuster, designated generally by the numeral 9, the push rod 10, and a valve rocker 11. Oil

from the engine lubricating system is pumped by means, not shown, to thelash adjuster 9 through the oil gallery 12 in the crankcase 1 and servesas `the hydraulic fluid for effecting the necessary lineal adjustmentswithin the lash adjuster to carry out its function of taking up lash inthe valve train.

As shown in Figure 2, the lash adjuster comprises a cylinder 13 in theform of an upwardly open cup which is laterally supported for slidingreciprocation in a bore 14 formed in the crankcase 1. Slidably receivedin the bore 15 of the lash adjuster cylinder is a plunger 16, also ofcup shape, whose upper end is closed by a push rod seat 17 on whichrests the lower end of the push rod 10. The opposite or bottom end of`the plunger cooperates with the bottom end of the lash adjustercylinder in defining an oil pressure chamber 18 in which is contained abody of oil for transmitting the engine valve opening movements betweenthese parts. Oil for supplying this chamber 1S is contained in thereservoir 19 formed by the interior of the cup-shaped plunger which, inturn, receives its oil supply from the oil gallery 12 (Figure l),through the ports 20, 21, 22 in the crankcase and lash adjuster cylinderand plunger, respectively, whose continuous intercommunication isassured by the grooves 23, 24 and 25 provided on the sliding surfaces ofthe cylinder and plunger.

The bottom end wall of the plunger 16 has an opening defined interiorlyof the plunger reservoir by a conical seating surface 27. Normallyengaging this surface and thereby closing the outer portion of theplunger opening is an annular check valve seat member 28, whose lowerend extends below the plunger and serves to pilot the open end of acup-shaped cage or retainer 29 for a ball check valve 31). The centralpassage 31 through this seat member 28 interconnects the reservoir 19with the pressure chamber 18, and its lower end forms the seat for theball 34). This ball` has freedom of ymovement between its seat at thelower end of passage 31 and the bottom of the cage 29 so as to act as acheck `valve which will accommodate flow of oil into the chamber 18, butprevent reverse flow. Oil flowing past 'the ball 30 when unseated maypass into the main portion of the chamber 18 through suitable apertures32 provided in the bottom end of the cage 29. AS shown, the upper end ofthis cage is externally flanged to abut the bottom face of the plunger,and is clamped thereagainst by a plunger return spring 33 resting on thebottom of the chamber 18 and tending to move the plunger outwardly ofthe lash adjuster cylinder. Carried within the plunger reservoir 19 is asecond spring 34 whose lower end abuts the check valve seat member 28,and whose upper end is suitably fixed as by abutment with an annularring 35. An outwardly expansible split ring 36 engages a groove in theplunger side wall to provide a removable support for the retainer 35.Spring 34 is of suflicient stiffness to normally maintain the checkvalve seat member 28 seated, as shown, but will yield in respouse to theforce of a predetermined pressure in chamber 18 acting against the ball36 and seat 28 to thereby limit the maximum pressure obtainabletherein.4

It is believed apparent from the above description that during engineoperation the oil which is trapped within the chamber 1S by the ballcheck valve 3i) operates in conventional manner as a noncompressiblebody for transmitting the cam lifted movement of the lash adjustercylinder to the plunger in effecting opening of the engine poppet valve5. During each such lift stroke some of the oil in the chamber 18escapes past the plunger between its outer periphery and the bore of thelash adjuster cylinder and enters the plunger reservoir 19 via itsgroove and port 22. As the lash adjuster returns to the base circle ofthe cam 7 following each lift stroke, the plunger spring 33 maintainsthe plunger against the push rod and the push rod, in turn, in operativeabutment with the en gine valve through the rocker 1I. Consequently,there is a certain amount of elongation of the lash adjuster during theperiod it is riding on the dwell portion of the cam, with attendant dropin pressure of the oil in chamber 1S which permits the ball to uncoverthe passage 31 in the check valve seat 28 and thereby allow sufficientoil to enrter the chamber 18 to replace that which escaped during thepreceding lift stroke. At the start of the next operating cycle thepressure again builds up in the chamber 18, causing the ball to againclose the passage 31, preparatory to opening the engine poppet valve 5.At relatively high engine operating speeds there is a tendency for theengine valve return spring 6 to surge and thereby lose its eectivenessin closing the poppet valve promptly after the lash adjuster returns tothe base circle of the cam. This has the effect of causing an excessiveelongation of the lash adjuster during such cam dwell periods, with theresult that the lash adjuster pumps up by accumulating too much oil inthe chamber 18 and aggravating and prolonging the condition of improperseating of the enginey poppet valve. However, by reason of the checkvalve seat being operative as a second plunger valve and to open againstits biasing spring 34, pressures which would otherwise develop in thechamber 18 incident to excessive opening of the poppet valve during thecam lift stroke are prevented. The raising of the check valve seatmember 28 from its seating Isurface Z7 on the plunger, it will be appreciated, is analogous in effect to increasing the rate of leakdown orleakage of oil between the plunger and the cylinder bore, and excessiveopening of the engine poppet valve and its consequent inability toreclose are thereby prevented.

While only a single preferred embodiment of the invention has beendisclosed, it is appreciated that numerous minor changes in theconstruction and arrangement of the parts may be made without departingfrom the spirit and scope of the invention as hereinafter defined.

I claim:

l. In a hydraulic lash adjuster including a generally cup-shapedcylinder having a bore, a generally cup-shaped plunger slidably fittingthe bore in nesting relation with the cylinder to define a uid pressurechamber between the respective bottom ends of the cylinder and plunger,

4 said plunger having an opening in its bottom end defined interiorly ofthe plunger by an annular seating surface, a check valve seat memberhaving an outer peripheral portion normally `seating on said plungersurface and having a passage for flow of hydraulic fluid into saidchamber, a check valve engageable with said seat member to block saidpassage against reverse flow therethrough and movable to engage saidseat member in response to chamber fluid pressures of less than apredetermined maximum, and biasing means supported interiorly of theplunger and acting to normally maintain said seat member engaged withsaid seating surface but yieldable to relieve chamber fluid pressures inexcess of said maximum.

2. In a hydraulic lash adjuster havin-g a cylinder and a plungerdefining a chamber for a body of fluid in thrust transmitting relationtherebetween, means accommodating enlargement and contraction of saidbody in the thrust direction including a passage in the plungerterminating with an opening to said chamber, a valve seat normallyrestricting said opening but movable inwardly of said passage toaccommodate flow from said chamber, biasing means opposing said movementof the valve seat but yieldable in response to the force of apredetermined chamber fluid pressure acting on said valve seat, and avalve engageable with said seat to normally block fluid flow from saidchamber but movable into said chamber to permit flow in the oppositedirection incident to enlargement of said body.

3. The invention defined by claim 2 wherein said plunger is hollow andsaid biasing means is in the form of a spring mounted interiorly of theplunger.

4. In a lash take-up device for transmitting movement between respectivedriving and driven means, a pair of members having surfaces opposingeach other in the direction of said movement and defining a fluidpressure chamber therebetween, one of said members having an opening forflow of fluid into and out of said chamber, a first valve for closing aportion of said opening and openable in response to a predeterminedpressure in said chamber, and a second valve for closing the remainderof said opening and closable in response to a lesser pressure in thechamber.

5. The invention defined by claim 4 wherein said portion and saidremainder of said opening are concentric with each other.

6. The invention defined by claim 5 wherein said first valve has anaperture defining said remainder of said opening.

No references cited.

